Nerf Mobile SAM damage a bit

The Mobile SAM has been shown to be exceptionally powerful in small groups, being able to annihilate large groups of helis. While the cost could be increased, it seems like a few changes for now would be good and mitigate some of the OPness.

Changes:
-Replace quick-firing 2-burst and replace it with 1 shot per second.
-Reduce damage to 32. This will make it kill Apaches in 4 shots instead of 3.
-Reduce missile speed from 426 to 341. (This will also effectively reduce range limit from 12.5 cells to 10).